Interpretive Summary: Beauveria bassiana is a fungus that infects Mormon crickets (Anabrus simplex Haldeman) and other grasshopper pests. B. bassiana strain GHA has been developed as a biological control agent. To measure the dose-dependent response of Mormon crickets to fungal attack, we applied B. bassiana strain GHA topically to adults using doses of 51,300 to 1.75 million conidia in sunflower oil, with oil only as a control. After three weeks, we assessed the survivors’ hemolymph for fungal cells, and measured the activities of two components of the Mormon crickets’ immunity: active phenoloxidase (PO) and lysozyme. Mortality increased and the body mass of survivors decreased with conidial dose. Survivors had elevated levels of PO relative to the controls. Survivors with fungal cells visible in their hemolymph did not differ in PO activity from those with clear hemolymph. We conclude that circulating PO may be an important enzymatic defense against Beauveria infection, and that it is associated with attempted clearing of Beauveria blastospores and hyphae from Mormon cricket hemolymph.

Technical Abstract:
Beauveria bassiana is an entomopathogenic Ascomycete fungus that serves as a biological control agent of Mormon crickets (Anabrus simplex Haldeman) and other grasshopper pests. To measure the dose dependent response of Mormon crickets to fungal attack, we applied B. bassiana strain GHA topically to adults using doses of 5.13x104 to 1.75x106 conidia in sunflower oil, with oil only as a control. After three weeks, we assessed the survivors’ hemolymph for fungal cells, active phenoloxidase (PO), and lysozyme. Mortality increased and body mass of survivors decreased with conidial dose. Survivors elevated PO activity to the same level independent of dose. Those with fungal cells visible in their hemolymph did not differ in PO activity from those with clear hemolymph. We conclude that circulating PO may be an important enzymatic defense against Beauveria infection, and that it is associated with attempted clearing of Beauveria blastospores and hyphae from Mormon cricket hemolymph.